Catalyst for chemical reactions in which participate carbon oxides



Patented Mar. 12, 1940 UNITED STATES PATENT o FFlCEI CATALYST FOR CHEMICAL REACTIONS IN WHICH PARTICIPATE CARBON OXIDES Giulio Natta, Milan, Italy No Application June 9, 1937, Serial No. 147,253. In Italy June 10, 1936 8 Claims.

principal constituents of many known catalysts which promote the following reactions:

It is, however, also known that zinc oxide prepared by ordinary methods, as well as commercial zinc oxide, is not suitable for practical realization of such reactions for the commercial production of hydrogen and methanol on account of its catalytic activity rapidly decreasing in the course of working. The reduction of catalytic activity in respect of useful reactions increases almost proportionately to the trend toward promoting secondary and noxious reactions.

A stronger and more lasting activity is sometimes obtained by adding promoters (in most cases metallic oxides) but as these are inert or noxious substances, from the catalytic standpoint, in respect of the desired reactions, their function is often simply protective on zinc oxide, and they often cause secondary reactions (formation of organic products of higher molecular weight in the synthesis of methanol, or formation of methane in such synthesis, or in the conversion of the carbon monoxide into hydrogen under pressure); p

Until now catalysts composed only of zinc oxide and having a lasting activity were little known. An exception was thezinc oxide obtained from smithsonite, but this is a natural product, which cannot easilybe obtained in pure form and which is not obtainable artificially in form of neutral, compact, and crystalline carbonate. All the types of zinc oxide prepared artificially show a catalytic activity which rapidly decreases in the course of time and further do not possess properties of mechanical resistance which are desired for catalysts for use on a commercial basis.

It has been found now that by the calcinatlon at a low temperature (ZOO-350 C.) of organic zinc salts, the decomposing temperature of which is higher than their melting temperature, products can be obtained which show a catalytic activity which is very strong and very durable. For instance zinc acetate (melting temperature 240) decomposes at nearly 280-300 and produces an excellent catalyst. After thecalcination has been performed, the catalyst composed essentially of zinc oxide, is agglomerated and has after grinding a granular porous structure and favorable mechanical properties. This particular structure is due to the fact that zinc oxide segregates from a melted mass, the melting temperature of the acetate being lower than 240 and it is produced, therefore, as a porous and agglomerated mass (not in form of powder as the calcined and precipitated products). On

account of this physical structure, no further zinc) appear in form of powder and do not show the same advantages from the catalytic point of view as the products obtained by calcination of fusible organic zincsaltsi'for instance zinc acetate).

The catalysts now proposedhave a very high grade of activity for the synthesis of methanol by reaction of carbon oxide with hydrogen under pressure, and may be used as well for the production of hydrogen by reaction of carbon monoxide with steam, in some cases under pressure.

For this reason they are preferred to any catalyst obtained by precipitation of zinc salts with alkali, which have a minor specific activity for the synthesis of the methanol and promote secondary reactions on account of the presence of traces of alkali, which arestrongly retained in the precipitates and cannot be removed by simple washing.

I It is wellknown that the presence of alkali,

or even traces of same, promotes the formation lisation, it is sufficient to heat at relatively low temperatures (nearly 300) for the preparation of the catalyst. .The zinc acetate first melts and then decomposes according to the following reaction: (CHzCOO)2ZI1=ZI1O+CO2+CH3COCH3.

The acetone which is formed according to the preceding reaction can be recovered thus reducing the cost of production of the catalyst, which is already low.

It will be convenient to carry on the reaction at the lowest possible temperature, in an atmosphere of inert or reducing gas, at normal pressure or still better, at a higher pressure.

If during the preparation of the catalyst pure zinc acetate is not used and substances are present which do not combine with the zinc oxide, at a low temperature, these substances can be noxious to the use of the catalyst, if they cause specific unfavourable reactions, especially byqprQ- -motin secondary reactions, which areinot'deesired. Thus, the presence of metals of the iron group, which are often present in the zinc ores, is noxious.

lic zinc in powder.

These metals are, however, easily; eliminated from the neutral solutions? of zinc salts using an excess of zinc oxide and of metal-' y; ne.= i g a id pre ete ib heating anhydrous n ac atezu ti 4 from m lten state.

"BrA cataIySt" containing oxides of' zinc and15 b her: maa.1. h .=1tas a reduced under the melts and then decomposes conditions.ingwhiclrthe catalyst is used, all said oxides being prepared by heating anhydrous orga'nic saltsof iinc and said other metals whose On the other hand, -the ,,presenc e, ofoxide s which are not reduced under theponditions which the catalyst isbeing used, as the alurninum Beside being activein respect ofktheflreactions stated above for the synthesisiof methanol and for the production of=.s'hydrogen, this, type pfi catalyst is also active in respect ofotherreactions in which participate carbon monoxide and car.- bon dioxide for instance? 1 s 1 nooongcoz-ftm H I I v CH3COOH+HCOOH;CH3QHO+1320+CO3 and many similar reactions, in which ketones and aldehydes are formed and simultaneousl carbon. dioxide is developed.

san :hyd 'Q Q,

lower than che aqecqmms a. 3 1 a 1 State.

,yical reactions in whichrhYdl'OUSJZlDC zacetate; untilatzzmelts and-:then "d8 composes; fromfimoltenist'ate.

r for chemical reactionsiinuwhich paigticipateicali V pbon oxides. and:hydrogen;iwhichicomprisesrpre ,metalslwvhi'chicannot be reduceduundenatherco ditionsin whichz-thecatalystrisqusedvthy:heating" a mixture ofranhydrous'. organictsal-ts ofizinccandrl lerr: said othere: metals whose; melting apoints 'arewbem 1 r s-o ea no an 1 ,5. A method forbre J participate carboir oxides l beats-s ats and hydrogen; :rwhic'h: .;comprises.1theatingnan i 31 6. A?'procsssfori the s'pl'eparatlonmof.

- paring alanixtiire iOfiOXideSi: on zinc-z larldr. othe The catalysts now proposedcanalsoadvan tageously beused for carrying onreactions, under pressure,=because, they do not promote noxious reducingreactions, which are highly favoured by pressure, as the formation of methaneby reducin carbon monoxide with hydrogen and the formation of elementary carbon by simultaneous oxidation and reduction. of ,the carbon monoxide only (2CO=C+COz .i

On account oftheir property of favouring the conversion of water gas as well as the synthesis of methanol from carbon monoxide and hydrogen;- under the same temperature and pressure the.

Lil-i681 reactions iii'which :participate'i carbom-oxide low their. decomposmg atem-peratures, untilisal salts melt and then-decomposeifrom'moltenstate :7. A processi-for; prepafingrcatalystst:fontchem.

and hydrogem which. -.comprise's: iheatingo unde "pressure' anhydrous organic -zinc="isa;ltsnhalvingi.za-

' melting point loweritharr-their decomposing tern -peratures, until said' s'alts' melt "and their 'ec'o'm catalysts now proposed make it possible to use 1.

in the synthesis of methanolwater gas with a lower hydrogen content thanthat which would apr m 'q' hixt'ufe be requiredtheoretically. This-lack of hydrogen. may be remedied by adding a small :quantity of steam, so that the two interdependent equilibri ums' allow the practical. realisation of, the fol-,.,.-

I until said saltssalts of 'zinc' s'iaidotlie" m'e pointsare below thein'de'co'mpos'ing tempefture me 

